1. Field of the Invention
This invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having such an electrode structure that a sealant can be easily cured.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) device controls the light transmissivity of liquid crystal cells in accordance with video signals to thereby display a picture corresponding to the video signals on a liquid crystal panel having the liquid crystal cells arranged in a matrix pattern. To this end, the LCD device includes an active area having the liquid crystal cells arranged in an active matrix type, and driving circuits for driving the liquid crystal cells in the active area. More specifically, the LCD device includes a lower plate in which thin film transistors for switching the liquid crystal cells, driving circuits for driving the thin film transistors and signal lines connected between the driving circuits and the thin film transistors are mounted on a lower substrate; an upper plate having color filters coated on a upper substrate in correspondence with the matrix liquid crystal cells in such a manner to be separated for each cell area by a black matrix stripe, and transparent electrodes coated on the surfaces of the color filters; a spacer provided between the upper plate and the lower plate to assure a certain cell gap; and a liquid crystal cell filled in a space defined between the upper and lower plates by the spacer. Such a liquid crystal display device is fabricated by preparing the upper plate and the lower plate separately to adhere them to each other and then injecting a liquid crystal through liquid crystal injection holes provided at the side portion thereof, and thereafter by coating the liquid crystal injection holes with a sealant and then curing the sealant. In this case, the sealant is cured by irradiating an ultraviolet ray continuously from the side portion and the rear portion after the coating. A reason why an ultraviolet ray is not irradiated from the front portion is because the color filters are coated on the upper substrate to prevent an ultraviolet ray from being transmitted. If the sealant is left alone as it is after the coating upon mass production of the LCD device, however, the sealant with a viscosity flows into the interior thereof. Accordingly, when an ultraviolet ray is irradiated from the side portion and the rear portion of the LCD device, metal signal wiring mounted on the lower substrate shuts off an ultraviolet ray irradiated from the rear portion and thus the flowing sealant is left without being completely cured to react on the liquid crystal, thereby causing a problem in that a stain is produced on the screen. Hereinafter, the above-mentioned problem in the LCD device will be described in detail with reference to the accompanying drawings. FIG. 1 and FIG. 2 is a plan view and a perspective view showing a portion of the LCD device 10 provided liquid crystal injection holes 22, respectively. In FIG. 1, first to third signal wiring 14, 16 and 18 are arranged at the outer area 28 of an active area 26 in which thin film transistors and pixel electrodes are mounted on a lower plate 12. A seal 20 coated with an adhesive and injection holes 22 for injecting a liquid crystal are provided in a desired shape. The first signal wiring 14 is gate row lines for applying a low-level voltage to gate lines in the active area 26, the second wiring 16 is redundancy lines, and the third wiring 18 is common voltage lines for applying a common voltage. After the lower plate having the structure as described above and the upper plate 30 prepared separately were arranged in position and adhered to each other with the aid of the seal coated with an adhesive, a liquid crystal is injected through the liquid crystal injection holes 22 provided at the side portion. The liquid crystal injection holes 22 are sealed by coating the liquid crystal injection holes 22 with a sealant 24 with a viscosity and thereafter curing the same by a continuous irradiation of ultraviolet ray (UV) before the sealant 24 flows into the interior thereof. In this case, since a major area of the upper plate 30 of the LCD device 10 is coated with the color filters to shield a UV, the UV is usually irradiated from the side portion and the rear portion of the LCD device as shown in FIG. 2.
By the way, if the LCD device is left alone for more than a certain time after coating of the sealant upon its mass production, the sealant flows into an area in which the first to third signal wiring 14, 16 and 18 are arranged. In this case, since the signal wiring arranged on the lower plate, particularly, the third signal wiring 18 adjacent to the liquid crystal injection holes 22 shuts off a UV irradiated from the rear portion of the LCD device, there occurs a phenomenon that the sealant 24 flowing into the third signal wiring 18 is not cured and thus flows into the active area 26. Accordingly, the sealant flowing into the active area 26 reacts on the liquid crystal to thereby cause a problem in that a stain is generated on the screen.